The present invention is an apparatus for heating liquids using a rotor and housing featuring indentations therein that induce cavitation bubbles in the liquid. The heat generated when these bubbles rapidly collapse is transferred to the fluid. Thus, the apparatus permits efficient heat transfer to a fluid without a solid heat exchanger interface.
There are a variety of devices that use mechanical energy to increase the temperature and/or pressure of fluids. Some of these prior art devices heat the fluid through friction between the fluid and the walls of a rotor and housing. In other prior art designs, mechanical agitation of the liquid generates heat. U.S. Pat. No. 3,791,349 to Schaefer discloses an apparatus to produce steam pressure by inducing shock waves in a distended body of water. U.S. Pat. No. 4,277,020 to Grenier describes a rotor and housing assembly where fluids are heated by shearing and friction between the walls of a rotor and housing containing circumferential indentations. Prior patents to the inventor of the present disclosure disclose a method of heating fluids through the production of shock waves in the liquid, where shock waves are induced by pumping a liquid into an enclosed chamber and spinning a rotor containing cylindrically-shaped dead-end bores. Venturi tubes are also used to induce cavitation in liquids.
Mechanically-induced cavitation is a well-known phenomenon, first encountered in the late 19th century during investigations into ship propeller design. Rapid motion of propeller blades through water produces a low-pressure region near the surface of the propeller blade that results in transient bubbles being formed: a process now known as cavitation. The subsequent rapid implosion of cavitation bubbles caused by the high ambient water pressure results in the generation of enormous turbulence, heat, and pressure. The temperature generated during the collapse of a cavitation bubble can exceed 5000 degrees Celsius.
Although cavitation is generally undesirable in marine propulsion applications, various devices have been employed for the last few years for the production and implosion of cavitation bubbles for research in ultrasound, acoustical cavitation for chemical processes and related fields.
The apparatus described herein is intended for applications in fluid purification, distillation, and even pasteurization. Conventional technologies for purification, distillation, and pasteurization typically involve direct heating of a fluid. In direct heating, heat exchange occurs at a solid interface between a heat source and the subject fluid. In other words, as a fluid flows through a heat exchanger, heat is transferred to the fluid via direct contact between the fluid and the wall of the heat exchanger. However, direct heating has a number of disadvantages. First, direct heating results in heat exchanger scaling or coking. This necessitates relatively frequent maintenance to remove the scaling or coking. In the pasteurization context, direct heating can result in scorching and destruction of the product to be pasteurized.